1. Field of the Invention
The present invention relates to an apparatus and method for detecting a time-frequency code in a Multi-Band Orthogonal Frequency Division Multiplexing Ultra Wideband (MB-OFDM UWB) system; and, more particularly, to an apparatus and method for easily detecting a time-frequency code that is currently in use in an MB-OFDM UWB system using time-frequency codes.
This work was supported by the Information Technology (IT) research and development program of the Korean Ministry of Information and Communication (MIC) and the Korean Institute for Information Technology Advancement (IITA) [2006-S-071-01, “Development of UWB Solution for High Speed Multimedia Transmission”].
2. Description of Related Art
As well-known in the art, an MB-OFDM UWB system uses the same time-frequency codes between systems constituting a piconet. The piconet refers to a radio Ad hoc communication system that enables a plurality of independent data devices to communicate with each other. The concept of such a piconet is illustrated in FIG. 1. A new device should detect time-frequency codes being used in the piconet in order to access thereto. That is, it should first detect the time-frequency codes and then receive beacon data, to thereby communicate data with other devices within the piconet in synchronism with them.
In the MB-OFDM UWB system, band groups 1 to 4 consisting of three subbands use time-frequency codes for seven kinds of channels. A time-frequency code for each channel of the band group 1 of the MB-OFDM UWB system is as follows:
TABLE 1Type ofChannelpreambleTime-frequency code (length = 6)11123123221321323311223344113322551111116622222277333333
For example, the type 1 of preamble is used for the channel 1, and its pattern is transmitted while performing frequency hopping in order of frequency bands 1, 2, 3, 1, 2, 3. The meaning of the frequency hopping according to time is shown in FIG. 2. FIG. 2 represents the frequency hopping according to time, for example, for channels 1, 3, and 6.
A preamble refers to a preset signal which is added in front of section of data to be transmitted and used to detect received signal, adjust the magnitude of a signal, correct frequency error and time error, and the like. The MB-OFDM UWB system has a total of 30 preambles, wherein the first 24 symbols are used to transmit the preambles shown in Table 1 and the other 6 symbols are used for channel estimation of a modem equalizer.
When a new device is registered in a piconet that is currently organized and wants communications, the device has to detect a time-frequency code that is currently in use in the piconet. This process is carried out at a Media Access Control (MAC) layer that controls a physical layer. The MAC layer allocates time more than a beacon interval and receives a signal for a constant time-frequency code. If the signal is demodulated for that interval to read information of the beacon frame, it is determined as a time-frequency code that is currently in use in the piconet. Since the number of types of channels is 7, this process requires scanning works seven times. In each step, the MAC layer and the physical layer continuously communicate control signals and data signals with each other, and therefore, the control is troublesome because of scanning works seven times.
In addition, for the channels 1 to 4, frequency hopping is performed according to time, and when a hopping time of current channel and that of a device desired to access differ from each other, it is impossible to receive a signal. Therefore, there is a need for a method for effectively solving the above problem and detecting time-frequency codes.